Conventional smoothing bars include a steel channel holder fitted with a wooden strip insert, to which a felt or high density foam pad layer is stapled or glued. A graphite coated paper is then wrapped around the assembly and stapled to the wooden strip. This conventional construction is intended to allow the sanding belt to slip across the smoothing bar with less friction and heat build-up. There are, however, several problems associated with this conventional construction. For example, the smoothing bars wear out very quickly, up to four times per eight hour shift (as many as 12 shut-downs per day). In addition, the soft construction does not give adequate profile control of the boards since the boards being sanded may well be harder than the smoothing bar. As a result, the boards will deflect the smoothing bar and the sanding belt, resulting in sanded boards being thinner on the edges than in their centers, and with variable "waviness" in the finished surfaces.
Ultrasmooth finishes and precise dimensions are particularly important to laminators and furniture manufacturers, as well as to the manufacturers of high quality plywood, MD fiber board and hard board. As a result, a new smoothing bar construction is desirable which overcomes the problems associated with the conventional bars as described above.
The object of this invention, therefore, is to provide a new smoothing bar construction which enables precise dimensional specifications to be achieved with consistency, and which is substantially more reliable and durable so that considerable cost improvements can also be achieved by eliminating the necessity for spare smoothing bars and associated down time required to change the bars.
In accordance with a preferred embodiment of the invention, the smoothing bar includes an elongated aluminum bar machined to height, width and face profile dimensions. The bar includes a belt face, a mounting face and a pair of angled side faces. The belt face is clad with zirconia ceramic tiles which are epoxied to the bar with heat curable epoxy. The resulting substantially continuous ceramic surface is ground smooth and flat, parallel with the mounting face of the aluminum bar. The mounting face, opposite the belt face, is fitted with a hexagon steel key to locate and hold the smoothing bar in the sander's adjustable smoothing bar platen. The hexagon key permits the smoothing bar to be installed without modification to a commercially available Kimwood sander as a direct replacement for the conventional smoothing bar.
The aluminum bar is drilled through, with two parallel holes extending through the entire length of the bar. These holes, which provide cooling passages, are tapped at either end for receiving hose end connectors so that air under pressure can be supplied to both ends of the bar. The two cooling passages are intersected at spaced locations along the length of the bar with air shower holes drilled perpendicular to the cooling passages (when viewed from above), but also at an angle to the belt face plane of the bar. The air shower holes open along the angled side faces of the bar so that the cooling air is discharged directly towards the back face of the belt, so as to clean the latter upstream and downstream of the bar.
The following advantages accrue as a result of the presently disclosed ceramic air-cooled smoothing bar:
(a) smoothing bar life is estimated to be 8 to 12 months versus 2 to 4 hours as in the conventional construction with savings in both manpower and machine down time;
(b) the regrindable ceramic tile finish allows for renewal at least once before recladding is required;
(c) the cooling air/shower stabilizes the bar profile and cleans dirt/dust from the sanding belt's surface, thereby preventing build-up or impingement between the bar and the belts;
(d) the zirconia ceramic tiles are abrasion-resistant, thermally stable, and do not build up with belt resin or dirt;
(e) the one-piece aluminum clad construction is solid and allows for even profile sanding of any width board, without variances in caliber between edges and centers of boards, even after continuous days of running; and
(f) no increase in horsepower is required due to the ceramic "hard" bar. In some applications, due to the rigidity of the ceramic bar, it is in fact possible to use less sanding pressure to achieve the finish and profile required and therefore reduce the actual power usage.
Thus, in its broadest aspects, the invention relates to a smoothing bar for use in a sanding apparatus comprising an elongated metal bar formed to include a belt face, a mounting face and a pair of opposite side faces, at least one cooling passage extending lengthwise of the bar from one end of the bar to the other; and a plurality of air holes arranged along the length of the cooling passage, substantially perpendicular to said cooling passage.
In another aspect, the invention relates to a smoothing bar for use in a sanding apparatus comprising an elongated metal bar formed to include a belt face, a mounting face and a pair of opposite side faces, a plurality of ceramic tiles adhered directly to the belt face; at least one cooling passage extending lengthwise of the bar from one end of the bar to the other; and a plurality of air holes arranged along the length of the cooling passage.
In accordance with still another aspect of the invention, there is provided in a sanding apparatus including a drive roll, at least two feed rolls, a guide roll, and an endless belt arranged to engage each of the rolls to thereby define a closed loop; and a smoothing bar located between the two feed rolls with a back side of the belt passing over the smoothing bar, the improvement comprising the smoothing bar constructed of an elongated metal bar having a mounting face, a belt face and a pair of side faces; at least one cooling passage formed in the bar and extending longitudinally from one end of the bar to the other, and a plurality of air shower holes arranged to discharge cooling air onto the back side of the endless belt.
Additional objects and advantages of the invention will become apparent from the detailed description which follows.